According to the known state of the art for the manufacture of ceramic bricks, a starting material consisting of clay in a proportion of at least 40% to 50% by weight and fillers, for example sand, in a proportion of at most 50% to 60% by weight, is prepared in a mixer with the addition of water. This gives a starting material which has a plastic consistency and which is fed to an extrusion press. The string issuing from the press is, immediately after it has emerged, divided into brick blanks by means of a cutting device, for example, a cutting harp. These blanks are then placed on boards on transport cars which convey them into a drying chamber where they are dried.
After shrinkage of the blanks has been substantially completed by this drying step and the blanks have thus reached the mechanical strength necessary for the subsequent handling, they are put next to one another in layers on burning cars, by means of which they are passed through a heating and firing kiln. The heating is necessary to avoid stresses being caused by the subsequent firing which is carried out at a temperature from about 800.degree. C. to 1100.degree. C. After firing is a cooling stage and then the fired hollow bricks are taken from the burning cars and are stacked, for example on pallets, for transport.
This known process has the following disadvantages:
The necessity of transferring the dried blanks from the transport cars to the burning cars is labour intensive.
High energy losses occur in particular because the blanks cool after drying and, during the separate charging and emptying of the drying chamber and the firing kiln, heat is lost therefrom.
Since the string is divided into individual blanks, which are dried and fired only subsequently, immediately after the string has issued from the press, there is a risk of the final products not being sufficiently dimensionally accurate.
Since the dried blanks are transported in the firing kiln on the burning cars which have a large mass, heating of the latter requires considerable energy which is lost during the subsequent cooling of the burning cars.
Due to the handling of the undried or dried blanks, deformations or damage occurs, resulting in a relatively high reject rate.
Due to the usual high issuing speed of the string from the press, about 20 cm/sec, strains and stresses can arise in the blanks and can, during the subsequent processing lead to damage, in particular cracks, or to fractures.
Since the load areas of conventional burning cars have a length of, for example, 2.5 m and a width of up to 6 m and are loaded with dried blanks up to a height of about 1.50 m, the volume thus formed or the size of the cross-sectional area formed by the blanks lying next to one another, as compared with the cross-sectional area of an individual brick, makes it impossible to achieve uniformity during firing. Rather, optimum values can be maintained only for a relatively small zone, that is to say for a small number of blanks. On the one hand, this leads to energy losses. On the other hand, the requisite uniformity in the properties of the finished fired bricks is not ensured.
The starting material from which conventional bricks are made has a high clay content and, in view of the fact that the shrinkage during drying or firing amounts to about 5% to 10% of the clay content, this has a large adverse effect on the dimentional accuracy of the finished fired bricks.
Finally, conventional processes require a drying chamber and a separate heating or firing kiln, which means high investment costs for the complete plant.
The present invention seeks to provide a process and apparatus for the manufacture of articles consisting of ceramic material which avoids the above listed disadvantages. This process is intended not only to enable bricks but also a large number of other articles consisting of ceramic material to be produced, and additional special effects should also be achievable.